US2161790A - Electrode for vacuum tubes - Google Patents

Description

June 13, 1939'.

J. B. J. ABADIE ELECTRODE FOR VACUUM TUBES Filed Aug. 17, 1934 biagwn. P1551452;

Patented June 13, 1939 PATENT OFFICE 2,161,790 ELECTRODE For VACUUM TUBES Jean Baptiste Joseph Marcel Abadie, Paris,

France, asslgnor of one-half to Lumineies (Societe a responsabilite limitee), Paris, corporation of France France, a

Application August 17, 1934, Serial No. 740,301

10 Claims.

Attempts have been made for a long time past to employ the electrodes of the class of Wehnelt electrodes, consisting of a wire coated with salts of the alkali metals or of the alkaline earth metals, in tubes (or bulbs) containing a rarefied atmosphere.

Such electrodes cannot be thus employed. The bombardment of the positive ions destroys the layer ofsalts by the formation of a cathode spot, which formation is concerned with the change of 1 the physical state of the body, such as volatilization, dehydration, or decomposition.

The electrodes which are the subject-matter of the present invention do not consist, as before, of a wire'or a metallic support coated with salts, but of a surface alloy between the metal which forms a support and the alkali metals or alkaline earth metals. The metals of these groups are well known to exhibit high electron emitting activity when used as electrodes in vacuum tubes and are so designated in the claims.

The Wehnelt electrodes may indeed be employed in high vacuum tubes or 'bulbs (such as wireless bulbs) as there is no bombardment by positive ions and hence no destruction of the salts, but they cannot be used in a rarefied atmosphere; on the contrary, the electrodes of the alloy type, the subject-matter oi the invention, may be employed in both cases, and will aflord, in bulbs without gaseous atmosphere, all emissions, without danger of any disengagement of gas.

Such electrodes will thus be characterized by the fact that they do not consist of a support coated with a salt, but consist of metallic alloy formed of the support and of alkali metals or I alkaline earth metals. Y

For the obtainment of the desired result, two different methods may be indicated by way of example.

First method.-In this method, the supporting metal (a metal having a high melting point) such as iron, nickel, molybdenum, tungsten, etc. is employed; it is heated by a blowpipe in the oxidizing part of the flame, thus forming a layer of the oxide of the metal of the support; the said support, while still at a red heat, is immersed in a powdered mixture of oxides or salts of the alkali metals or alkaline earth metals of which the metal is to be alloyed with the metal of the support. This affords a surface layer which is then treated with, that is, reheated by the blowpipe, The coating thus becomes pasty, and spreads around the support.

It is preferable to use compounds of the alkali metals or the alkaline earth metals, for instance,

In France August 26, 1933 in the state of oxides. The oxidized layer of the supporting metal makes an intimate connection with the layer of oxides of the alkali metals or the alkaline earth metals.

Second method-The coating is formed by the wet process and not by the dry process. Use is made of an electrodeconsisting of the oxidizing supporting metal; this oxidized electrode is treated in an electrolytic bath consisting of salts of alkali metals or of alkaline earth metals. When the coating has been formed, one proceeds, in the vacuum lamp itself, with the reduction of these salts in an atmosphere of hydrogen, by a direct or an indirect heating, or by the action of a high tension electric discharge.

It is evident that since the layer upon the refractory metal consists of intimately commingled oxids of the coating metal or metals, as these oxids are reduced to metal they will immediately unite and, because of the high temperature atv As the reduction of the metals proceeds, the

metal of the support assimilates with the metals in the coating and an electron emitting surface integrated with the metallic conduction support is thus provided.

The properties of the alloys thus obtained appear to obey the general physical laws governing the physical characteristics of alloys; in particular, the properties are remarkable when eutectic alloys are obtained. For the electrodes having.

only a small output and hence not possessing any great energy due to the bombardment of the pos"-" 'itive ions, it is preferable to-use salts of potassium, sodium, rubidium, or caesium. For el'ectrodes having a large output, and in order. to prevent the decomposition of the'alloy by the volatilization of the alkali metal, use will be made of metals such as barium calcium etc. (alkaline A mixture which gives good re;

earth metals). suits consists of of a barium salt, of a strontium salt, of a-calcium salt (oxides). In

order to increase this emission, it is feasible to add radio-active substances in the form of their salts, and these will be reduced at the same time as'the salts of the alkali metals and the alkaline earth metals (thorite) The salts of the alkali metals and the alkaline earth metals may be combined, for intermediate bardment by the positive ions.

This effect can be obtained as long as the cathodic fall of potential is below a certain value,

which is designated the tension of disintegration,

or disintegration voltage. The tension of disintegration usually amounts to about volts. This aifords a lower limit of trode.

If the temperature of the electrode is too high, the alloy will be decomposed, the alkali metal or the alkaline earth metal will be volatilized, and

- the electrode will lose all is properties- There- -moval of metal;

fore there will be a maximum temperature and current which must not be exceeded. These limiting factors depend upon .the calorific capacity and the cooling of a given electrode;

The accompanying drawings show various embodiments of the invention.

Fig. 1 is a diagram of the fall of cathode tension for a given electrode.

Figs. 2 and 3 relate wheat-protected electrodes in conformity with the invention.

Fig. 4 relates to the application of the invention to a low-tension tube adapted for alternating current operation.

Fig. 5 shows the use of the invention with modulating bulbs adapted for television.

' i 6 relates to the use of the invention for the emission of light from a point, between two ad jacent beads.

Fig. -7 shows a similar use, with a bulb which is spontaneously lighted.

Fig. 8 relates to an application of the same kind.

Fig. 9 shows an embodiment comprising an auxiliary electrode.

Fig. 1 shows the form of the curve indicating the value of the fall of tension at the cathode,

with reference to the value of the current, for a given electrode; theoutput which may be used in this electrode will vary between the values i and i, which output corresponds to a fall of potential less than Cd.

By choosing the value of the current between these two values, the duration of the electrode is practically unlimited, as well as the duration of the tube, as there is no absorption due to a re- The fall of potential at the cathode is particularly low (between 6 and 30 volts).

In order to reduce to a minimum the expenditure of energy at the cathode for giving off the electrons, it is preferable to provide the electrode with a non-conductor of heat; Figures 2 and 3 represent electrodes thus provided with non-conductors.

In Fig. 2, I represents the passage of the wire in the glass, and this wire has a spiral part at the end, which is surrounded'by a bead 2 of the emitting mixture above indicated; the size of the bead may be from 1 to 10 mm At 3 is shown the surrounding part, consisting, for example, of Pyrex glass, outside of the passage I. With the use of a refractory earth in the plastic state, such as silicate. of alumina, kaolin, powdered silica,

current for a given elecv etc, there is produced a sleeve 4 having a tubular part i. The refractory sleeve thus formed is then heated by the blowpipe to a bright red. The cylindical part 5 is not indispensable, but it has a certain importance in the operating of the electrode; the loss of energy in this part of the positive device furthers the rise of temperature of the bead 2 which is necessary for the emission of this latter.

Instead of a refractory sleeve, it is feasible to employ an emitting body which has the same features and serves both for emission and for heat protection. 1

Fig. 3 shows a modification of the cathode represented in Fig. 2. In this case, the spiral part is replaced by a small hollow cylinder 6 made of a metal such as molybdenum, copper, tungsten; nickel, iron etc.

Fig. 4 shows a low-tension tube adapted for direct working upon alternating current. The electrodes I and 8 may be the same as in Figs. 2 and 3, or may consist of two hollow cylinders of a refractory metal, filled with an emitting mixture and surroundedbyarefractorycrucible. The operation of the are at each electrode is assured by a transformer 9 and by an auxiliary electrode III which serves for the ionizing and for the heating of the electrode. The calorific energy of the electrode for the continuous operation of the tube, in spite of the break due to each period of the current.

Such continuity cannot be practically obtained with the known electrodes with cathode spot.

Fig. 5 represents theuse of one of the aforesaid electrodes for the construction of modulating lamps for television. The anode, in this case,

forms a metallic ring I I surrounding the cathode I2, and the lamp sends out its modulated light on I the axis of the electrode.

Such electrodes, when heated directly by the flow of current in the metal support,-or indirectly, may form cathodes for rare gas bulbs or for rectifying bulbs.

These same electrodes adapted for direct or indirect heating, may be used in bulbs for wireless transmission or receiving, and in general, in all apparatus in which it is necessary to employ an emission of electrons, such as Kenotrons, .Thyratrons, X-ray tubes, canal ray tubes, etc.

A spiral part which is coated and produced in conformity with the present invention may serve as an auxiliary electrode for output, for the obtainment of pointolyte bulbs aifording a source of light concentrated in a point.

Such a bulb may be formed according to Fig. 6, in which I3 and II are two beads of tungsten, between which the arc is to be produced; I5 is a spiral part which is coated and is treated according to the invention, and I6 is a two-metal band, that is, a metallic band composed of two strips having diflerent expansions and thus bending under the action of heat. When the bulb is cold,

. the two-metal band I 6 makes contact for the flow of current in the coated spiral l5: by the effect of the heating due to the spiral, the two-metal band will bend, thus breaking the circuit; the arc is formed between the spiral I 5 and the electrode,

the spiral is coated, it effects its emission at a low red heat.

A second example of pointolyte bulb is shown in Fig. '7; I1 and I8 are tungsten electrodes, and i9 is an auxiliary electrode which may consist of calcium, which latter has the advantage of completely purifying the rare gas forming the atmosphere of the bulb (neon, argon); 20 is an auxiliary electrode which is treated according to the invention, and 2| is a fine wire resistance which connects l9 and i1 and is embedded in the lamp base.

When employing a difference of potential of 110 volts, the ionisation takes place between is and 20; the arc is formed between 20 and I1, and then proceeds'froni II to I 8.

Another application consists in the use of two electrodes 22 and 23, these being juxtaposed in a bulb according to Fig. 8. This affords a bulb without filament, which lights up spontaneously at 110 volts. Such bulbs can be modulated, and can be used for projecting apparatus. They will have different colours according to the metallic vapours which can be placed in the bulb: mercury, cadmium, etc.

As they are without inertia, they can be modulated, and may be employed for projection apparatus, for telephony by visible or invisible rays (infra-red, ultra-violet), or for television. The modulated power which can be used in this case, may attain 100 to 500 watts without difiiculty.

In Fig. 8, if one of the electrodes 22-23 isreplaced by a carbonanode, for instance, one alternation is cut off, and this affords a rectifying bulb.

Fig. 9 represents a bulb in which the electrode 24 is connected with the electrode 25 by a resistance 26. At 110 volts, an arc is formed spontaneously between 24 and 21, and thus the electrode 24-is now in the state of emission, and the arc is then formed with 25. This provides a long positive stream, and this bulb may be employed for the obtainment of metallic vapour lamps, for instance with vapour of the alkali metals (sodium vapour).

In the claims, for the sake of brevity, the word refractory replaces the expression metal having a high melting point found on page 1', line 41, column 1.

Since the first step in the manufacture of the electrode is oxidation of the supporting metal, it is evident that only oxidizable refractory metals are useful, and all such will serve. The supportmg metal is, therefore, designated in the claims as being oxidizable".

I claim:

1. The process of manufacture of electrodes of high electron emissive power which comprises profoundly oxidizing at least a portion of a metal support, covering said oxidized portion with a layer of material selected from the group consisting of oxides of the alkali and alkaline earth metals and salts of the alkali .and alkaline earth metals which yield oxides on heating, and powder of the material of the metal support, agglomeratingsaid layer by fusing it and maintaining it in fused condition until it has profoundly penetrated the pores of the oxidized portion of said metal support, then placing the product in a reducing atmosphere and then heating it to the temperature at which the oxidized metal support and the said agglomerated material will reduce to metallic condition and a profoundly alloyed surface will be formed upon said metal support.

2. The process of manufacture of electrodes of high electron emissive power which comprisesdeeply oxidizing a metal support, depositing a layer of material selected from the group consisting of the oxides and salts of the alkali and alkaline earth metals upon the surface thereof by feeble electrolysis, then reducing this said layer and said oxide to metallic condition, then heating it to the temperature at which it forms a profound alloy with the material of the metal support.

3. An electrode of high electron emissive power, comprising a metal support chosen from the group of refractory metals consisting of tungsten, molybdenum, nickel and iron, said metal support carrying an electron emissive portion comprising an alloy of a plurality of electron emissive metals chosen from the group consisting of the alkaline earth metals and alkali metals, said alloy being itself profoundly alloyed with the metal support.

4. The electrode of claim 3 modified in that the alloy between the metal support and the alloy of electron emissive metals consists largely of a eutectic mixture.

5. Electrodes of claim 3 in which the ratio between the alkali metal and the alkaline earth metal in the alloy varies inversely with the output in amperes per square centimeter of emitting surface for which the electrode is to be used.

6. The process of claim 2 in"which the alloying temperatures to which the electrode is heated is such as to favor the formation of eutectic mixtures upon the electrode.

7. The method of making an electron emissive electrode which comprises the steps of oxidizing at least a portion of a metal support, coating the oxidized portion with a layer of material containing the oxides and salts of the alkali metals and the alkaline earth metals which are capable of yielding oxides when they are heated, fusing the material of said layer onto said metal support, and heating the metal support so treated in a reducing atmosphere to a temperature at which the oxidized metal of the support and the oxides in the layer upon it are reduced to metallic condition, and the metal of the support assimilates the metals of the layer.

. metal and an alkaline earth metal.

9. An electrode of high electron emissive power comprising a support of spiral formation made from a metal selected from the group consistin of tungsten, molybdenum, nickel and iron, said support carrying an electron emissive portion comprising an alloy of metals chosen from the group consisting of alkali metals and alkaline earth metals, said alloy itself being profoundly integrated with the metal of the support.

10. An electrode of high electron emissive power comprising acup-shaped element made of a metal selected from the group consisting of tungsten, molybdenum, nickel and iron, said element carrying an electron emissive portion comprising an alloy of metals selected from the group consisting of alkali metals and alkaline earth metals, said alloy being profoundly integrated with the metal of the said element.

JEAN BAPTIB'I'E JOSEPH MARCH: ABADIE.

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